- Is taking tricyclic, selective serotonin reuptake inhibitor (SSRI) or serotonin and noradrenaline reuptake inhibitor (SNRI) antidepressants for PHN (or for indications other than pain) and the dosage has been changed within 14 days of the Treatment Visit. Only subjects on stable doses from at least 14 days prior to the Treatment Visit through the duration of the study will be eligible to participate